Mass spectrometry (MS) is a major discovery tool in the life sciences. By using this analytical technique it is possible to analyze the molecular composition of a sample by ionizing the sample or the analyte molecules contained in said sample and then measuring the mass-to-charge ratios of the resulting ions. The mass spectra obtained by an MS experiment are used to identify, characterize, and quantify the abundance of the analytes of interest. In particular, liquid chromatography-mass spectrometry (LC-MS) has recently been used for quantification of drugs and biologically active compounds, mostly because of the high selectivity, sensitivity, speed, and simplicity imparted by LC/MS/MS.
For quantification of a target analyte in a sample, it is generally necessary to first establish a calibration curve which represents the relationship between the analytical signal obtained from the particular analytical method used, e.g., peak area or peak height in MS spectra or in mass chromatograms, and the quantity of the target analyte. Thus, prior to the analysis of a sample the analytical signals of a series of calibration standards (e.g., the isolated target analyte in six different concentrations) have to be determined and this external calibration has to be done regularly (e.g., daily). However, this procedure reduces productivity, increases the costs per sample, and moreover, renders the analysis of just one sample inefficient.